This invention relates to the field of alcohol-based fuel products and flame-coloration components therein.
None of the references cited herein are admitted to be prior art to the present invention, but are provided solely to assist the understanding of the reader.
Ethanol has become an increasingly popular fuel which, when denatured, can be commercially sold for use in, for example, alcohol stoves. Ethanol is also used in combination with other fuels such as gasoline to produce "gasahol". Denatured ethanol (such as standard denatured alcohol-SDA 3-A which includes 5 volumes of methanol combined with 100 volumes of ethanol) burns cleanly in air in an open container or dish, producing a partially blue, principally yellow flame which is visible in bright sunlight. Although the yellow color may suggest oxygen limitation, no soot or volatile organic compounds (VOCs) are produced.
Several commercially available fuels utilize denatured ethanol diluted with water, perhaps the most common ones combining denatured ethanol, water, and a gelling agent. For example, one gelled fuel contains approximately 65-70% by volume ethanol, and is packaged in metal cans which can be placed under food vessels such as chafing dishes and then ignited (e.g., Sterno.RTM.-brand fuel manufactured by Colgate-Palmolive, Tenafly, N.J.). The lack of flame visibility with this fuel and other similar water-containing alcohol-based fuels can lead to accidental burn injuries and fire damage because of the lack of awareness that the ethanol is burning. While it might seem straightforward to add something to ethanol to make its flame visible, there are severe limitations on the use of such an additive. For example it should be of low toxicity and substantially non-polluting, i.e., low in emission of volatile organic compounds, as the fuel burns. Such an additive should also persist in the ethanol as long as any combustible ethanol remains, i.e., throughout the burning cycle of the ethanol, so that flame coloration is sustained.
Several ethanol-based fuel compositions which contain a variety of chemicals for producing flame coloration and for increasing the fuel's flash point (above the ethanol flash point of 55.degree. F.) have been described. For example, Badger in U.S. Pat. No. 4,405,336 describes an alcohol fuel composition containing a final concentration of ethyl alcohol ranging between 79.4% and 87.7% by volume, formulated from at least 90%, i.e., 180 proof ethyl alcohol. The maximum concentration of water in the composition is 8.85% by volume. The composition contains a mixture of methyl isobutyl ketone, kerosene, xylenes, and isopropanol. The isopropanol is present at a level of between 1.6% and 4.3% final concentration. All of the ingredients are reported to raise the flash point and increase the visibility of the flame. The xylenes and the isopropanol are reported to mask odors. However, the overall composition is highly toxic (e.g., xylene) and irritating to the skin, and produces a significant amount of smoke and volatile organic compounds when burned.
Balland et al. in FR 2,690,689 describe a flame coloring system for an alcohol burner. A coloring salt such as a borate is added to the liquid, solid or gelled alcohol fuel, e.g., methanol, ethanol or propanol, which is positioned at the appropriate air flow inlet. Successful flame coloration depends upon the positioning of the coloring agent relative to air flow apertures in the burner. The salts are used at high concentrations, e.g., 2-20% by volume or weight, and are either very caustic (NaOH) and corrosive to burner hardware, or are toxic and polluting as metal salts (copper, strontium, antimony).
In JP 4,065,489, a fuel is described which generates a colored flame. The fuel contains a 1-4 carbon lower alcohol (methanol, ethanol, propanol, or butanol), up to 15% by weight water, and water-soluble salts which function as flame colorants when added at moderately high concentrations. The metal salts tend to be orrosive to burner hardware, and add cost to the fuel.